Spin electronics element and method of manufacturing thereof

ABSTRACT

A structure used in the formation of a spintronics element, the spintronics element to include a plurality of laminated layers, includes a substrate, a plurality of laminated layers formed on the substrate, an uppermost layer of the plurality of laminated layers being a non-magnetic layer containing oxygen, and a protection layer directly formed on the uppermost layer, the protection layer preventing alteration of characteristics of the uppermost layer while exposed in an atmosphere including H 2 O, a partial pressure of H 2 O in the atmosphere being equal to or larger than 10 −4  Pa, no other layer being directly formed on the protection layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. application Ser. No. 15/064,586, filed onMar. 8, 2016, and allowed on Apr. 18, 2019, the entire disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to an spin electronics element and methodof manufacturing thereof.

In recent years, among various types of non-volatile memory, a memoryusing an MTJ (magnetic tunnel junction) element, which is a spintronicselement and which is also a resistive recording element, is drawingattention for its high rewriting resistance, high CMOS (complementarymetal-oxide semiconductor) compatibility, three-dimensional integrationproperty, and the like.

FIG. 1A shows an MTJ element in a low resistance state, FIG. 1B shows anMTJ element in a high resistance state, and FIG. 1C shows a variableresistance equivalent to the MTJ element. As shown in FIGS. 1A and 1B,the MTJ element (the element labeled “MTJ”) includes a free layer FR, afixed layer FI, and a tunnel barrier TB.

The tunnel barrier TB is made of an insulating thin film such as MgO orAl₂O₃. The free layer FR and the fixed layer FI are each made of aferromagnetic material such as iron, cobalt, or an alloy thereof. Thefree layer FR has an upper electrode terminal TE, and the fixed layer FIhas a lower electrode terminal BE. The magnetic direction of the freelayer FR changes in accordance with the flow of electric current throughthe MTJ element, but the magnetic direction of the fixed layer FI doesnot change.

As shown in FIG. 1A, when the magnetic direction of the free layer FRand the magnetic direction of the fixed layer FI are the same(parallel), the MTJ element enters the low resistance state. On theother hand, as shown in FIG. 1B, when the magnetic direction of the freelayer FR and the magnetic direction of the fixed layer FI are opposite(antiparallel), the MTJ element enters the high resistance state. InFIGS. 1A and 1B, the magnetic directions of the free layer FR and thefixed layer FI are indicated with the broken arrows.

The low resistance state and the high resistance state of the MTJelement can be switched between each other by applying an appropriatelevel of current to the MTJ element. When the MTJ element is in the highresistance state as shown in FIG. 1B, by supplying current I_(mtj)flowing from the free layer FR to the fixed layer FI, the MTJ elemententers the low resistance state as shown in FIG. 1A. If the currentI_(mtj) is supplied when the MTJ element is in the low resistance state,the low resistance state is maintained.

On the other hand, when the MTJ element is in the low resistance state,by supplying current −I_(mtj) flowing from the fixed layer FI to thefree layer FR, the MTJ element enters the high resistance state as shownin FIG. 1B. If the current −I_(mtj) is supplied when the MTJ element isin the high resistance state, the high resistance state is maintained.Thus, the MTJ element can be regarded as a variable resistance as shownin FIG. 1C.

By letting the high resistance state represent one of two logical values“0” and “1” and letting the low resistance state represent the other,the MTJ element can function as a recording element. FIG. 2 is a diagramshowing the R-I characteristics of the MTJ element. As shown in FIG. 2,the R-I characteristics of the MTJ element exhibit hysteresis, andtherefore, the low resistance state and the high resistance state of theMTJ element are maintained even after the supply of current to the MTJelement is stopped. This allows the MTJ element to function as anon-volatile recording element. In FIG. 2, Rp indicates the electricalresistivity of the MTJ element in the low resistance state, and Rapindicates the electrical resistivity in the high resistance state.

The MTJ element can also function as a switching element by letting thelow and high resistance states correspond to ON and OFF states,respectively.

Spintronics elements such as the MTJ element are configured to have aferromagnetic layer, and a non-magnetic layer such as a MgO layer asdescribed above. MgO is hygroscopic, and the following study tocharacterize the initial current leakage spots in the MgO layer has beenconducted: a 1 nm-thick CoFeB film was formed on the MgO layer, and theinitial current leakage spots in the MgO layer was evaluated using ascanning probe microscope having a conductive cantilever attached to it(C. Yoshida, et. al, IRPS 2009, p. 139).

However, the present inventors have discovered that the 1 nm-thick CoFeBfilm formed on the MgO layer does not prevent alteration or degradationof characteristics of a MgO layer. An MgO tunnel insulating film in thespintronics element has a problem in that the characteristics of thefilm change due to the reaction with not only CO₂ but also H₂O whenexposed to the atmosphere. In order to solve this problem, the presentinvention is aiming at providing a spintronics element and a method forits manufacture, in which, even when a wafer having a non-magnetic layersuch as a MgO layer at the uppermost layer thereof is exposed to theatmosphere, alteration and/or degradation of characteristics of thenon-magnetic layer can be prevented.

SUMMARY OF THE INVENTION

The invention is applied to a method of manufacturing a spintronicselement from a plurality of laminated layers, the method including thesteps of (a) forming a plurality of laminated layers in firstmanufacturing equipment, (b) forming a first wafer in the firstmanufacturing equipment, including applying a protection layer directlyon a non-magnetic uppermost layer of the plurality of laminated layersso that the protection layer prevents alteration of characteristics ofthe uppermost layer, and (c) exposing the first wafer to an atmosphereoutside of the first manufacturing equipment, the atmosphere includingH₂O, a partial pressure of H₂O in the atmosphere being equal to orlarger than 10⁻⁴ Pa.

The invention is also applied to a structure used in the formation of aspintronics element, the spintronics element to include a plurality oflaminated layers, including a substrate, a plurality of laminated layersformed on the substrate, an uppermost layer of the plurality oflaminated layers being a non-magnetic layer containing oxygen, and aprotection layer directly formed on the uppermost layer, the protectionlayer preventing alteration of characteristics of the uppermost layerwhile exposed in an atmosphere including H₂O, a partial pressure of H₂Oin the atmosphere being equal to or larger than 10⁻⁴ Pa, no other layerbeing directly formed on the protection layer.

The invention is also applied to a spintronics element, including anunderlayer, and four laminated layers formed by binding at least twowafers, including a first ferromagnetic layer formed on the underlayer,a non-magnetic layer formed on the first ferromagnetic layer, a secondferromagnetic layer formed on the non-magnetic layer, and a cap layerformed on the second ferromagnetic layer, wherein a surface portion ofthe second ferromagnetic layer directly contacts the cap layer and isfree of any layer having no magnetization.

According to the present invention, a protection layer that allows forexposure to the atmosphere is formed on the uppermost layer, which is anMgO layer, for example, to prevent the alteration or degradation ofcharacteristics of the uppermost layer under the protection layer, whichbroadens horizon of the spintronics element manufacturing process.

The above and other objects, features and advantages of the presentinvention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing an MTJ element in a low resistance state,FIG. 1B is a diagram showing an MTJ element in a high resistance state,and FIG. 1C is a diagram showing a variable resistance equivalent to theMTJ element.

FIG. 2 is a diagram showing the R-I characteristics of the MTJ element.

FIG. 3A is a diagram showing a substrate of a spintronics element, andFIGS. 3B to 3G are diagrams showing the specific configurations of thesubstrate.

FIG. 4 is a schematic diagram for explaining a method of evaluationusing a scanning probe microscope (SPM).

FIG. 5 is a diagram showing a comparison example in which a protectionlayer is not formed on the uppermost layer of the element layer.

FIGS. 6A and 6B are diagrams schematically illustrating respectivesamples B and C that were prepared, each having a stack structure.

FIG. 7 is a flowchart showing the method of manufacturing the samples.

FIG. 8A is a graph showing the results of an X-ray photoelectronspectroscopic (XPS) analysis of the surfaces of samples having a CoFeBprotection layer, and samples not having a CoFeB protection layer, andFIGS. 8B and 8C are schematic diagrams of samples without and with theprotection layer.

FIG. 9A is a graph showing the results of an XPS analysis of the surfaceof the MgO layer in the comparison examples without a protection layerin which each MgO layer has a different thickness, and FIG. 9B isschematic diagrams of the comparison examples.

FIGS. 10A to 10C are graphs showing the results of a spectrum analysisof Comparison Example 5 and Working Examples 1 and 2, respectively.

FIGS. 11A and 11B, FIGS. 12A and 12B, FIGS. 13A and 13B, and FIGS. 14Aand 14B show the topography and current of Comparison Examples 5 and 6,and Working Examples 1 and 2, each having a CoFeB protection layer, thatunderwent annealing at 400 degrees and were subjected to a conductiveAFM evaluation, respectively.

FIG. 15 is a schematic diagram for explaining the process of anexemplary embodiment.

FIG. 16 is a flowchart showing the process of the exemplary embodiment.

FIG. 17 is a schematic diagram showing a binding process of an exemplaryembodiment.

FIG. 18 is a flowchart of a process of an exemplary embodiment.

FIG. 19A is a diagram for explaining a conventional process of aspintronics element having a double junction structure, and FIG. 19B isa diagram for explaining a process of manufacturing the spintronicselement by binding a plurality of substrates using the process of anexemplary embodiment.

FIGS. 20A and 20B are diagrams for explaining the manufacture of aspintronics element of the quad junction structure.

FIGS. 21-23 are diagrams for explaining the manufacture of three othertypes of spintronics element of the quad junction structure.

FIGS. 24A and 24B are diagrams for explaining the manufacture of aspintronics element having the double reference structure.

FIGS. 25A, 25B and 25C are diagrams for explaining the manufacture of amagnetic domain wall motion type memory element.

FIGS. 26A and 26B are diagrams for explaining the dead layer.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, a description will be given, while referring to the drawings,of an embodiment of the invention. In order to solve the above-mentionedproblem, the present inventors have conducted studies resulting in thediscovery that when a wafer having a non-magnetic uppermost layer suchas MgO layer needs to be exposed to the atmosphere, or in other words,when the wafer needs to be exposed to the atmosphere in which a partialpressure of H₂O is equal to or larger than 10⁴ Pa, by forming aprotection layer that prevents alteration or degradation ofcharacteristics of the uppermost layer of the wafer at least immediatelybefore exposing the wafer to the atmosphere, alteration ofcharacteristics of the non-magnetic layer can be prevented even in theabove-mentioned atmosphere. In the description below, the non-magneticlayer that has a risk of alteration or degradation of characteristics isan MgO layer, and the protection layer is a CoFeB layer, but thenon-magnetic layer that has a risk of alteration or degradation ofcharacteristics is not limited thereto. That is, the protection layer isnot limited to a CoFeB layer, but may be made of a material selectedfrom among Co (cobalt), Fe (iron), CoB, FeB, and CoFeB. The protectionlayer may be a layer that contains at least one of Co, Fe and B (boron),and at least one of Ni (nickel), Zr (zirconium), Hf (hafnium), Ta(tantalum), Mo (molybdenum), Nb (niobium), Pt (platinum), Cr (chromium),Si (silicon), and V (vanadium).

Exemplary Embodiment 1

First, a spintronics element of an exemplary embodiment 1 of theinvention will be explained. Examples of the spintronics element includea magnetic head used for a magnetic disc, but not limited thereto. FIG.3A shows a spintronics element substrate 1 of exemplary embodiment 1. Inthis specification, the spintronics element substrate 1 encompasses allof the following: the substrate in the process of manufacturing thespintronics element, the substrate after the manufacturing process; andthe substrate having the protection layer of the exemplary embodiment 1formed thereon in the process of manufacturing the spintronics element.

As shown in FIG. 3A, the spintronics element substrate 1 includes an MTJ(magnetic tunnel junction) element layer 10 made of two or morelaminated layers, and a protection layer 30 made of CoFeB or the like.At the uppermost layer of the element layer 10, or in other words, theuppermost layer on which the protection layer 30 is formed, anon-magnetic layer 20 made of MgO or the like is formed. That is, thespintronics element substrate 1 of the exemplary embodiment 1 has astructure in which laminated layers at least including a ferromagneticlayer and a non-magnetic uppermost layer 20 are formed on a substratethat is not shown in the figure, and on this non-magnetic uppermostlayer 20, the protection layer 30 is formed. In this specification, thenon-magnetic layer 20 is also be referred to more specifically as MgOlayer 20. However, the non-magnetic layer 20 is not limited to an MgOlayer, and may be any non-magnetic layer containing at least oxygen. Itis preferable that the non-magnetic layer contain oxygen and Mg. Theelement layer 10 may also have another structure such as a stackstructure in which an underlayer made of Ta or the like is formed on asubstrate, and a ferromagnetic layer and a non-magnetic layer arelaminated thereon, or a structure in which an active element such as aCMOSFET is formed on a Si substrate, and interconnect layers or the likefor connecting the active element to the MTJ element are formed thereon.

Interfacial magnetic anisotropy perpendicular to the plane of the layersat the non-magnetic layer and the ferromagnetic layer interface occursby controlling the temperatures of the annealing process and thethickness of the ferromagnetic layer, and is able to orient themagnetization of the ferromagnetic layer in a direction perpendicular toa plane of the layers (film plane). The annealing temperature may differfrom materials in the ferromagnetic layer that contains at least onetype of other 3d transition metal, such as CoFe or Fe. The magnetizationdirection can be changed from being parallel to perpendicular withrespect to the plane of the layers by suitably controlling the filmthickness for the material. The cause of the magnetization directionbecoming perpendicular to the film plane is due to the interfacialperpendicular magnetic anisotropy at the interface of the non-magneticlayer and the ferromagnetic layer. By forming a thin layer bycontrolling the thickness of the ferromagnetic layer on an atomic layerlevel, the ratio of volume in which the interfacial perpendicularmagnetic anisotropy is present relative to the volume of theferromagnetic layer can be increased. Thus, the interfacialperpendicular magnetic anisotropy at the interface between theferromagnetic layer and the non-magnetic layer becomes pronounced suchthat the magnetization direction becomes perpendicular to the plane ofthe layers. The effect is particularly increased at the interfacebetween an oxygen-containing compound represented by MgO, Al₂O₃, SiO₂,or the like, and a ferromagnetic material containing at least one typeof 3d transition metal, such as Co or Fe, whereby the magnetizationtends to be more easily oriented in the direction perpendicular to theplane of the layers. The interfacial magnetic anisotropy perpendicularto the plane of the layers at the non-magnetic layer and theferromagnetic layer interface is explained in the disclosures of U.S.Pat. Nos. 8,917,541, 9,153,306, and 9,202,545, which are incorporatedherein by references.

FIGS. 3B to 3G are diagrams showing specific configurations of thespintronics element substrate 1. As shown in FIG. 3B, the spintronicselement substrate 1, for example, has an element layer 10 in which anunderlayer 11, a ferromagnetic layer (fixed layer) 12A, and an MgO layer20 are laminated in this order on a substrate such as an Si substrate,which is not shown in the figure, and on this element layer 10, aprotection layer 30 is formed. The ferromagnetic layer (fixed layer) 12Ais configured such that its magnetic direction is fixed in the directionperpendicular to the surface of the layer (upward or downward). As shownin FIG. 3C, the ferromagnetic layer (free layer) 13A may also be formedon the underlayer 11. The ferromagnetic layer (free layer) 13A isconfigured such that its magnetic direction is not fixed to either theupward or downward direction. The protection layer 30 is preferably madeof the same material as that of the layer immediately below theuppermost layer of the element layer 10, namely, the ferromagnetic layer12A in the example of FIG. 3B. If the ferromagnetic layer 12A is a CoFeBlayer, for example, it is preferable that the protective layer 30 bealso a CoFeB layer. When the protection layer 30 is made of CoFeB, it ispreferable that its thickness be equal to or greater than 2 nm asdescribed below.

Alternatively, as shown in FIG. 3D, the spintronics element substrate 1may have a structure in which an element layer 10 is formed bylaminating an underlayer 11, a fixed layer 14 (ferromagnetic layer 14A,a non-magnetic binding layer 14B, and a ferromagnetic layer 14C), and anMgO layer 20 in this order, and on this element layer 10, a protectionlayer 30 is formed. The ferromagnetic layer 14A and the ferromagneticlayer 14C are each configured such that its magnetic direction is fixedto the perpendicular direction (upward or downward). The non-magneticbinding layer 14B is a Ta layer, for example. The non-magnetic bindinglayer 14B may be a layer made of W (tungsten), Hf, Zr, Nb, Mo, Ti(titanium), Mg (magnesium), MgO, or the like. Alternatively, as shown inFIG. 3E, the spintronics element substrate 1 may have a structure inwhich an element layer 10 is formed by laminating an underlayer 11, afixed layer 14 (ferromagnetic layer 14D, a non-magnetic binding layer14B, and a ferromagnetic layer 14C), and an MgO layer 20 in this order,and on this element layer 10, a protection layer 30 is formed. Theferromagnetic layer 14D is configured such that its magnetic directionis fixed to be the downward perpendicular direction, and theferromagnetic layer 14C is configured such that its magnetic directionis fixed to the upward perpendicular direction. Alternatively, as shownin FIG. 3F, the spintronics element substrate 1 may have a structure inwhich an element layer 10 is formed by laminating an underlayer 11, afree layer 15 (ferromagnetic layer 15D, a non-magnetic binding layer15B, and a ferromagnetic layer 15C), and an MgO layer 20 in this order,and on this element layer 10, a protection layer 30 is formed. Theferromagnetic layers 15C and 15D are each configured to have a magneticdirection that is not fixed to either the upward or downwardperpendicular direction. Alternatively, as shown in FIG. 3G, thespintronics element substrate 1 may have a structure in which an elementlayer 10 is formed by laminating a magnetic domain wall motion layer 16and an MgO layer 20, and on this element layer 10, a protection layer 30is formed. The configurations described above are examples of thespintronics element substrate 1, and those configurations may becombined with each other.

As described above, in the exemplary embodiment 1, in a process ofmanufacturing the spintronics elements in which the uppermost layer is anon-magnetic layer made of a material such as MgO that changes inquality or degrades in an environment containing H₂O, CO₂, or the like,a protection layer that prevents alteration or degradation ofcharacteristics of the non-magnetic uppermost layer is formed, making itpossible to suppress the alteration or degradation of characteristics ofthe non-magnetic uppermost layer even when the element is exposed to theatmosphere containing H₂O, CO₂, and the like. This allows variousprocesses to be conducted that would significantly degrade thecharacteristics of the spintronics element if it weren't for theprotection layer.

Exemplary Embodiment 2

Next, an exemplary embodiment 2 will be explained. The spintronicselement substrate 1 used for a magnetic resistive memory element,magnetic sensor, or the like is exposed to the atmosphere, for example,during an inspection process of or after the manufacturing process. Itmay be in the middle of the manufacturing process in some cases, but asdescribed above, the MgO layer 20 changes in quality by absorbing H₂Oand/or by reacting with CO₂ in the atmosphere. Thus, if the spintronicselement substrate 1 having the MgO layer 20 formed at its uppermostlayer is exposed to the atmosphere, the characteristics of the MgO layer20 would change. In the exemplary embodiment 2, however, the protectionlayer 30 is formed on the MgO layer 20 to prevent degradation oralteration of characteristics of the MgO layer 20, and therefore, it ispossible to conduct an inspection process or the like. In the exemplaryembodiment 2 described below, a case where a product inspection isconducted during the manufacturing process will be explained.

As shown in FIG. 3B described above, in this example, the ferromagneticlayer 12A immediately below the MgO layer 20 is a CoFeB layer, and theprotection layer is made of the same CoFeB material. CoFeB/MgOperpendicular magnetic tunnel junction (p-MTJ) is a promising buildingblock of next generation non-volatile memory integrated in VLSI (T.Endoh, et al., VLSI Tech. Symp., p. 89, 2012, S. Ikeda, et al., Nat.Mater., vol. 9, p. 721, 2010). Thus, evaluating the current leak spotdensity distributed in the plane of the MgO layer 20 formed in theelement layer 10 shown in FIG. 3B, for example, is very important interms of evaluating the reliability of the spintronics element such as amagnetic tunnel junction element in which the MgO layer 20 functions asa tunnel insulating layer.

As a specific example of the product inspection, evaluation on thespintronics element substrate 1 by the conductive AFM (atomic forcemicroscopy) method using a conductive cantilever will be explained. Acharacterization of these leakage spots in an MgO tunneling barrier bymeans of conductive atomic force microscopy (c-AFM) provides usefulinformation for accurate modeling of p-MTJ (C. Yoshida, et. al, IRPS, p.139, 2009). FIG. 4 is a schematic diagram for explaining the method ofevaluation using a scanning probe microscope (SPM). The AFM device willbe explained below. AFM is one type of scanning probe microscopes, andby scanning the surface of the spintronics element substrate 1 with asharp end of a probe (conductive cantilever b1), and by converting theatomic force detected by the probe to an electric signal, the surfaceprofile can be measured.

As shown in FIG. 4, the film forming equipment A and the scanning probemicroscope equipment B are generally provided as separate pieces ofequipment. This means that the spintronics element substrate 1 needs tobe moved out from a chamber of the film forming equipment A, and thespintronics element substrate 1 is thereby exposed to the outsideatmosphere. Thus, for example, when the leak spot density of the MgOlayer is to be tested for the product inspection in the middle of theMTJ film forming process, for example, because the film formingequipment A where the spintronics element substrate 1 is formed, and thescanning probe microscope equipment B are separate pieces of equipment,the spintronics element substrate 1 needs to be transferred from one tothe other, which causes the spintronics element substrate 1 to beexposed to the atmosphere.

A study shows that the leak spot density of such a spintronics elementsubstrate increases between the 5-minute mark and the 15-minute markafter the exposure to the atmosphere (K. M. Bhutta, Ph. D, Thesis inPhysics, Fakultät für Physik, Universitat Bielefeld, 2009), and thealteration of characteristics of the MgO layer 20 in the atmosphere isconsidered to have affected the measurement of the leak spot density.

Even if a nitrogen gas substitution device such a glovebox is installedin the transfer path of a sample, it is not possible to completelyeliminate H₂O. Because MgO absorbs moisture even in an atmosphere inwhich a partial pressure of H₂O is 10⁴ Pa (E. Carrasco, et. al, J. Phys.Chem. C 114, 18207 (2010)), the above-mentioned problem remains auniversal problem.

Furthermore, even if an environment-controlled SPM (which allows for avacuum state of the probe chamber or a change in atmospheric gas in theprobe chamber) is used, a sample is still exposed to the outsideatmosphere on the way to the environment-controlled SPM. Specialequipment in which the film forming equipment and the SPM equipment areconnected to each other via a transfer chamber that maintains ultra-highvacuum state may be configured, but the equipment size and cost wouldincrease.

In the exemplary embodiment, however, the protection layer 30 is formedon the MgO layer 20, which is the uppermost layer of the element layer10, and therefore, it is possible to prevent alteration and degradationof characteristics of the MgO layer 20. As a result, the current leakspot density on the MgO layer 20 can be accurately evaluated. Theprotection layer 30 has the function of preventing alteration ofcharacteristics of the MgO layer 20 even if the spintronics elementsubstrate 1 is exposed to an atmosphere in which a partial pressure ofH₂O is equal to or greater than 10⁻⁴ Pa.

The present inventors have discovered the following facts using X-rayphotoelectron spectroscopy. That is, in a case of forming a CoFeB film30 as the protection layer on the MgO layer 20, in order to preventalteration of characteristics of the MgO layer 20 caused by reactionwith H₂O or CO₂ in the atmosphere:

(1) the protection layer needs to be 1 nm or greater in thickness toprevent the reaction with CO₂ in the atmosphere; and

(2) the protection layer needs to be 2 nm or greater in thickness toprevent the reaction with H₂O in the atmosphere.

The reasons thereof will be explained next. As shown in FIGS. 5, 6A, and6B, three samples A, B, and C each having a stack structure wereprepared. Sample A shown in FIG. 5 is an example (comparison example) inwhich a protection layer is not formed on the uppermost layer of theelement layer. In each spintronics element substrate, an SiO₂ substrate101, a 10 nm-thick Ta layer 102 as a non-magnetic layer, a 10 nm-thickCoFeB layer 103, and an MgO(x) layer 20 with the thickness t_(MgO) being0.4, 0.8, 1.2, or 3.0 nm are formed in this order. That is, fourdifferent samples (will be referred to below as Comparison Examples 1 to4) in which the thicknesses of MgO(x) layer 20 differ from each otherwere prepared.

Sample B shown in FIG. 6A includes an MgO layer 20 of the same thicknesst_(MgO) (1.2 nm) (hereinafter referred to as MgO (1.2 nm)), and on topof that, a CoFeB(x) layer 130 with the thickness t_(CoFeB) being either1.0, 1.5, 2.0, or 3.0 nm is formed as the protection layer. The samplein which the thickness t_(CoFeB) of the CoFeB(x) layer 130 (protectionlayer) is 1.0 nm is Comparison Example 5, the sample in which thethickness t_(CoFeB) of the CoFeB(x) layer 130 (protection layer) is 1.5nm is Comparison Example 6, the sample in which the thickness t_(CoFeB)of the CoFeB(x) layer 130 (protection layer) is 2.0 nm is WorkingExample 1, and the sample in which the thickness t_(CoFeB) of theCoFeB(x) layer 130 (protection layer) is 3.0 nm is Working Example 2.

In Sample C shown in FIG. 6B, the thickness of the CoFeB layer, which isthe protection layer 30, is fixed to 2 nm, and the thickness t_(MgO) ofthe MgO(x) layer 20 is either 0.8, 1.2, or 1.6 nm. The respectivesamples with the thickness t_(MgO) of the MgO(x) layer 20 being 0.8,1.2, and 1.6 nm are Working Example 3, 4, and 5, respectively (see Table1).

TABLE 1 Layers CoFeB MgO(x) CoFeB(x) Reaction Reaction sample (10 nm)t_(MgO) t_(CoFeB) with CO₂ with H₂O Comparative 10 nm 0.4 nm N/APositive Positive Ex. 1 Comparative 0.8 nm N/A Positive Positive Ex. 2Comparative 1.2 nm N/A Positive Positive Ex. 3 Comparative 3.0 nm N/APositive Positive Ex. 4 Comparative 1.2 nm 1.0 nm Negative Positive Ex.5 Comparative 1.2 nm 1.5 nm Negative Positive Ex. 6 Example 1 1.2 nm 2.0nm Negative Negative Example 2 1.2 nm 3.0 nm Negative Negative Example 30.8 nm 2.0 nm Negative Negative Example 4 1.2 nm 2.0 nm NegativeNegative Example 5 1.6 nm 2.0 nm Negative Negative

FIG. 7 is a flowchart showing the method of manufacturing the samples.As shown in FIG. 7, the samples of working examples and comparisonexamples shown in the figures were formed by magnetron sputtering onthermally grown SiO₂ film at room temperature (Step 1). Thereafter,these samples were exposed to the atmosphere in a clean room for twodays or longer to obtain the equilibrium of the surface reaction, forexample, the surface oxidation and the moisture absorption (Step 2).Then, the samples were annealed at 400 degrees for two hours in vacuum(Step S3). For the c-AFM measurement, the cleaved samples were fixed ona metal plate, and conductive paste was on the cleaved edge of thesample and the plate. A positive bias voltage was applied to the plateduring the c-AFM measurement. Another cleaved sample was subjected toX-ray photoelectron spectroscopic (XPS) analysis using Al Kα radiation(Step S4).

The test conditions may be described as follows.

Angle resolved X-ray Photoelectron Spectroscopy (XPS)Al Kα radiation (hν=1486.6 eV)Take-off angles=30°, 45°, and 72°.Charge neutralizer was used.

Conductive AFM

A PPP-EFM tip coated with PtIr (R=25 nm) was used.The tip was grounded, and the positive bias voltage was applied to thebottom electrode of the samples.

<MgO and CO₂ Reaction>

FIG. 8 is a graph showing the results of XPS evaluation of the surfacesof samples having a CoFeB protection layer (Comparison Example 5,Working Examples 1 and 2), and samples not having a CoFeB protectionlayer (Comparison Example 2: MgO layer is 0.8 nm thick). FIG. 8 showsthat Comparison Example 2, i.e., the sample with no protection layer,exhibits a characteristic peak in the carbonate bonding (J. F. Moulder,P. E. Sobol, and K. D. Bomben, Handbook of X-ray PhotoelectronSpectroscopy (Physical Electronics, 1995), p. 40-41). On the other hand,in Comparison Example 5, Working Example 1 or 2 in which the protectionlayer was formed to be 1, 2, and 3 nm, carbonate was not confirmed. WhenMgO reacts with CO₂ in the atmosphere, MgCO₃ is formed (Y. Yanagisawa,et al., J. Phys. Chem. 99, 3704 (1995)), and therefore, this resultshows that it is possible to suppress the reaction between MgO and CO₂by the formation of a 1 nm-thick protection layer.

<H₂O and MgO Reaction>

FIG. 9A is a graph showing the XPS analysis results on the surface ofthe MgO layer in the samples without a protection layer in which eachMgO layer has a different thickness (Comparison Examples 1 to 4). Fromthis results, the present inventors have made the following findingsregarding the Mg2p spectrum. That is, the layer designated M1 in FIG.9B, near 50.7 eV in FIG. 9A is an interface layer formed by the reactionbetween the underlying CoFeB and MgO that absorbed moisture, layer M2near 49.6 eV is MgO that absorbed moisture (Mg(OH)₂), and layer M3 near50.4 eV is MgO that absorbed no moisture. FIG. 9B shows schematicdiagrams of Comparison Examples 1 to 4. As shown in FIGS. 9A and 9B, inComparison Example 1 in which the thickness of the MgO layer is 0.4 nm,which is the smallest thickness, only layer M1 is formed. On the otherhand, in Comparison Examples 2 and 3, both layers M1 and M2 are formed.In Comparison Example 4 where the thickness of the MgO layer is 3.0 nm,which is relatively large, a part of the MgO layer did not absorb H₂O.As a result, layers M2 and M3 (MgO layers) were formed, but layer M1 wasnot formed.

Next, an Mg2p spectrum analysis was conducted on the MgO layer withprotection layer (Comparison Example 5, Working Examples 1 and 2), andthe results this analysis were compared with the XPS analysis resultsfor the surface of the MgO layer described above. FIGS. 10A to 10C aregraphs showing the spectrum analysis results of Comparison Example 5 andWorking Examples 1 and 2. As shown in FIG. 10A, in Comparison Example 5where the 1 nm-thick protection layer is formed, the layers M1 and M2are observed, which means that the MgO layer has absorbed moisture. Thatis, when a 1 nm-thick CoFeB film is used for the protection layer, it isnot possible to sufficiently prevent the MgO layer from absorbing H₂O.On the other hand, in Working Example 1 with the 2 nm-thick protectionlayer and Working Example 2 with the 3 nm-thick protection layer, onlythe M3 component is observed, which means that the MgO layer did notabsorb H₂O. This shows that, in order to prevent the reactions of theMgO layer with CO₂ and H₂O in the atmosphere, the protection layer madeof CoFeB needs to be at least 2 nm-thick. Furthermore, in WorkingExamples 3 to 5, i.e., the samples in which the MgO layer has differentthicknesses, the MgO layer did not react with H₂O or CO₂.

<Evaluation by Conductive AFM>

In conductive AFM, a conductive cantilever b1 is added to theconfiguration of the contact AFM device B, and by measuring current thatflows through the surface of a sample to the probe of the cantilever,the surface profile image and the current value image of the sample canbe provided at the same time. The samples having a CoFeB protectionlayer that underwent annealing at 400 degrees (Comparison Examples 5 and6, Working Examples 1 and 2) were subjected to the conductive AFMevaluation, and the result of each example of topography are shown inFIGS. 11A, 12A, 13A and 14A, respectively, and the result of eachexample of a current image are shown in FIGS. 11B, 12B, 13B and 14B,respectively. In the sample having a 1 nm-thick protection layer(Comparison Example 5) and the sample having a 1.5 nm-thick protectionlayer (Comparison Example 6), the surface roughness was greater and thecurrent image was flat in many areas, which indicates abnormal results.Those abnormal results were more pronounced in Comparison Example 5. Thehydration of the MgO layer appears to the inventors to have been thecause of this abnormality. On the other hand, in the samples having a 2nm-thick protection layer (Working Example 1) and 3 nm-thick protectionlayer (Working Example 2), the degree of surface roughness was small,and many current leak spots were observed. As a result, the leak spotdensity of the MgO layer was evaluated properly. That is, by forming theCoFeB protection layer to a thickness of 2 nm or greater, it waspossible to prevent the MgO layer from reacting with H₂O and CO₂ in theatmosphere, which would cause degradation.

Other Embodiments

In the description of the exemplary embodiment 2 above, an example inwhich an evaluation by a scanning probe microscope was conducted on theMgO layer in the middle of the manufacturing process of the spintronicselement substrate having the MgO layer was explained. However, theabove-mentioned exemplary embodiment 2 can also be applied to othertypes of inspections. When a spintronics element having an MgO layer atthe uppermost layer thereof is subjected to an inspection during orafter the manufacturing process, the spintronics element is exposed tothe atmosphere on the way from the film forming equipment to theinspection equipment, and therefore, a problem similar to the onedescribed above, i.e., alteration or degradation of characteristics of anon-magnetic uppermost layer of the element layer arises. To solve thisproblem, as described above, by forming the protection layer of theexemplary embodiment 2, alteration or degradation of characteristics ofa non-magnetic uppermost layer of the element layer can be effectivelyprevented.

Specifically, in addition to the inspection using a scanning probemicroscope equipped with a conductive cantilever, the spintronicselement substrate 1 can also be applied to a surface roughnessevaluation using a scanning probe microscope in a tapping mode. Themethod for keeping intermittent contact between a sample surface and avibrating cantilever is called Dynamic Force Microscopy (DFM). Further,the substrate 1 can also be applied to a film thickness measurement byspectroscopic ellipsometry, a film thickness measurement by XRR (X-rayreflectometer), a film thickness measurement by an XRF (X-rayfluorescence) device, or the like. Furthermore, other types ofevaluations and tests such as an evaluation using an optical microscope,a visual inspection, an evaluation by an XRD (X-ray diffraction) device,an evaluation by a CIPT (current-in-plane tunneling) device, anevaluation by an SEM (scanning electron microscope) device, and anevaluation of a sheet resistance on the spintronics element substrate 1are made possible.

Not only in the case where the element is subjected to evaluations andtests, but also in other cases where the element is moved from oneequipment to the other and a wafer container such as FOUP (front openingunified pod) or FOSB (front opening shipping box) is replaced, thisprotection layer can effectively prevent alteration of characteristicsof the uppermost layer.

Furthermore, when it is necessary to move the element from one piece ofequipment to another in various processes of manufacturing spintronicselements, such as heat treatment process, an electromagnetic radiationapplication process, a magnetic field application process, a lithographyprocess, a dry-etching process, a film forming process, an ionimplantation process, a plasma doping process, a wet-cleaning process,and a wafer binding process, there is a chance that the MgO layer willbe exposed to the atmosphere and alteration of characteristics can occurin a manner similar to the above. Thus, in the examples of moving thespintronics elements between pieces of equipment for any of themanufacturing described above as well, by forming the protection layer30 made of a CoFeB layer having a thickness of 2 nm or greater on theMgO layer 20, the alteration of characteristics of the MgO layer 20 canbe prevented.

After the inspection or transfer between two pieces of equipment iscompleted, and the spintronics element substrate 1 with the protectionlayer described above is in an environment where the MgO layer is freefrom the risk of alteration of characteristics due to H₂O and CO₂, theprotection layer is removed. That is, if the manufacturing process hasnot completed yet, the rest of the spintronics element is formed asdescribed below by conducting a film forming process and the like afterthe protection layer is removed. In the process of removing theprotection layer, it is preferable to leave at least one-atomic layer onthe MgO layer (surface) instead of completely removing the CoFeBprotection layer. This is because in the MTJ element, the magneticanisotropy (an interfacial magnetic anisotropy) is very important at theinterface between the non-magnetic layer including Mg and O and theferromagnetic layer including Fe or Co. This interfacial magneticanisotropy perpendicular to the plane of the layers at the non-magneticlayer and the ferromagnetic layer interface is able to orient themagnetization of the ferromagnetic layer in a direction perpendicular tothe plane layers. In particular, if the non-magnetic layer is a MgOlayer, and the ferromagnetic layer is a CoFeB layer, this one-atomiclayer plays an important role as the origin of the interfacialperpendicular magnetic anisotropy. When a ferromagnetic layer such as aCoFeB layer is formed on the MgO layer after the CoFeB protection layeris removed, the one-atomic layer has the important function of makingthe magnetic direction of the ferromagnetic layer perpendicular.

In the process of forming the rest of the spintronics element afterremoving the protection layer, the ferromagnetic layer may be formed byconducting a film forming process after removing the protection layer orby binding the spintronics element substrate with another spintronicselement substrate. By binding two spintronics element substratestogether to manufacture one spintronics element, it is possible toprovide a device of higher quality. Such an exemplary embodiment will beexplained below.

Exemplary Embodiment 3

In spintronic elements having a multi-layer structure, the crystalorientation or composition ratio of a film varies depending on the filmforming equipment, and therefore, in some cases, better characteristicscan be achieved by forming MTJ using a plurality of pieces of equipmentrather than a signal piece of equipment. Thus, in the exemplaryembodiment 3, a part of the MTJ element is formed by the equipment A,and then the rest of the element is formed by different equipment B.This exemplary embodiment 3 can be applied to the above-mentioned casein which a part of the spintronics element substrate 1 having theprotection layer is formed by the equipment A, and after the inspectionprocess or the like is conducted, the spintronics element substrate isreturned to the equipment A for the film forming process to complete thespintronics element. That is, the film forming equipment B used afterthe inspection process or the like may be the same as the film formingequipment A or may be different.

FIG. 15 is a schematic diagram for explaining the process of theexemplary embodiment 3. FIG. 16 is a flowchart showing the process ofthe embodiment 3. As shown in FIG. 15, in the film forming equipment A(of a plant A1 not shown), for example, a spintronics element substrate1 is manufactured up to the MgO layer of MTJ (FIG. 16: S11), and aprotection layer 30 is formed thereon to prevent the degradation of thesurface (FIG. 16: S12). Next, the spintronics element substrate 1 thathas undergone a necessary process such as inspection outside of theequipment A in a plant A1 (not shown) is shipped to a plant B1 (notshown). The spintronics element substrate 1 is exposed to the outsideatmosphere (FIG. 16: S13) during transfer, and then set in the equipmentB in the plant B1 (FIG. 16: S14). The plant B1 may be the same as theplant A1, and the equipment B may be the same as the equipment A.However, even if the equipment A and the equipment B is the sameequipment, as explained before, the spintronics element substrate 1 isexposed to the outside atmosphere when the inspection is performed.Next, the spintronics element substrate 1 set in the equipment Bundergoes a process to remove the protection layer 30 such asreverse-sputtering (sputter-etching) or plasma etching. In this process,at least a portion of the protection layer 30 that is directly incontact with the MgO layer 20 (on the surface), i.e., one-atomic layer30 a, is not removed (FIG. 16: S15).

When the protection layer was a CoFeB layer, the one-atomic layer 30 aexists as a CoFe layer. As described above, this CoFe layer is theorigin of the interfacial perpendicular magnetic anisotropy. When aferromagnetic layer such as a CoFeB layer is formed on the MgO layerafter the CoFeB protection layer is removed, the CoFe layer has theimportant function of making the magnetic direction of the ferromagneticlayer perpendicular. Even if the protection layer is made of a CoFeBlayer, because this one-atomic layer 30 a is a CoFe polycrystallinelayer, the presence thereof can be observed by an electronic microscopeor the like. That is, even if the ferromagnetic layer such as a CoFeBlayer is to be formed on the one-atomic layer 30 a, because theone-atomic layer 30 a has a crystal structure differing from that of theferromagnetic layer, the presence thereof can be confirmed using anelectronic microscope or the like. In the film forming equipment B, afirst recording layer 31 made of CoFeB, a Ta layer 32 functioning as thenon-magnetic layer, a second recording layer 33 made of CoFeB, and anon-magnetic layer 34 made of MgO, for example, are formed in thisorder, thereby completing the spintronics element (FIG. 16: S16).

As described above, in the exemplary embodiment 3, the spintronicselement substrate 1 is manufactured by the equipment A in the plant A1,for example, and then transferred to the plant B1 where a part of theprotection layer 30 is removed by the equipment B so as to leave atleast one-atomic layer 30 a. After that, the film forming process isresumed. That is, in the spintronics element substrate 1 having theprotection layer 30 of the exemplary embodiment 3, the alteration ofcharacteristics of the MgO layer 20 can be prevented by the protectionlayer 30 even during the manufacturing process, and therefore, it ispossible to ship the spintronics element substrate to a different plantincluding overseas locations. Because the films can be formed using aplurality of film forming equipment, spintronics elements of higherquality can be provided. In the above description of the exemplaryembodiment 3, a case in which the spintronics element is completed bytwo pieces of equipment was explained, but the protection layer 30 maybe formed as many times as necessary, for example, when the elementsubstrate is moved from one piece of equipment to the another, when aninspection is conducted on the element substrate, or the like.

Exemplary Embodiment 4

Next, an exemplary embodiment 4 will be explained. In the embodiment 4,an example of forming one spintronics element by binding together twoseparately-prepared spintronics element substrates will be explained.This manufacturing method provides spintronics elements with improvedcrystal orientation. The specific method will be explained below.

FIG. 17 is a schematic diagram showing a binding process of theexemplary embodiment 4, and FIG. 18 is a flowchart of the process. Asdescribed above, spintronics elements of a single junction, a doublejunction, and a quad junction include a plurality of metal layers andinsulating layers, and therefore, the physical characteristics (such ascrystal orientation and crystal particle size) differ between the upperpart and the lower part of the magnetic tunnel junction (MTJ), even ifthe two parts are made of the same material. For example, in the doublejunction, the crystal orientation of the upper MgO layer differs fromthat of the lower MgO layer. Also, in the double reference layer MTJ,the coercive force of the upper reference layer is smaller than that ofthe lower reference layer in some cases. By dividing MTJ into a top partand a bottom part or three or more parts, manufacturing the respectiveparts separately, and binding them together, the above-mentioned problemcan be avoided, and MTJ with even orientation and desiredcharacteristics can be obtained.

As shown in FIGS. 17 and 18, in the film forming equipment A, forexample, a spintronics element substrate 1 (first wafer) is manufacturedup to the MgO layer of the MTJ (FIG. 18: S21), and a protection layer 30is formed thereon to prevent the degradation of the surface (FIG. 18:S22). Next, the spintronics element substrate 1 that has undergone anecessary process such as an inspection is shipped to equipment C. Thespintronics element substrate 1 is exposed to the atmosphere (FIG. 18:S23) during transfer. The transferred spintronics element substrate 1 isset in the equipment C (FIG. 18: S24). The equipment C may be the sameas the equipment A.

On the other hand, in the film forming equipment B, a spintronicselement substrate (second wafer) 2 is manufactured. The spintronicselement substrate 2 includes a substrate not shown in the figure, and onthis substrate, a Ta layer as an underlayer, an MgO layer as anon-magnetic layer, a CoFeB layer as a first recording layer, a Ta layeras a non-magnetic layer, and a CoFeB layer as a second recording layerare formed in this order. The spintronics element substrate 2 is alsoexposed to the atmosphere during transfer, and therefore, a cap layer120 is formed to prevent degradation of the uppermost CoFeB layer. Thespintronics element substrate 2 is transferred and set in the equipmentC (FIG. 18: S25). The equipment B may be the same as the equipment C,and the equipment B may be the same as the equipment A.

Next, the spintronics element substrate 1 set in the equipment Cundergoes a process to remove the protection layer 30 such asreverse-sputtering (sputter-etching) or plasma etching. In this process,at least a part of the protection layer 30 that is in contact with theMgO layer 20 (on the surface), i.e., one-atomic layer 30 a, is notremoved (FIG. 18: S26). The cap layer 120 formed on the spintronicselement substrate 2 is removed as well. Then, the spintronics elementsubstrate 1 a after removing the protection layer 30 except for theone-atomic layer 30 a, and the spintronics element substrate 2 a afterremoving the cap layer 120 are bound together such that the respectiveexposed surfaces make contact with each other, thereby forming aspintronics element (FIG. 18: S27).

Other Embodiments

Next, another example of the spintronics element that is manufacturedthrough a binding process will be explained. FIGS. 19 to 25 areschematic diagrams for explaining the process. FIG. 19A is a diagram forexplaining a conventional process of a spintronics element having thedouble junction structure, and FIG. 19B is a diagram for explaining aprocess of manufacturing the spintronics element by binding a pluralityof substrates using the processes of the other embodiments. Similarly,FIGS. 20A and 20B are diagrams for explaining the manufacture of aspintronics element of the quad junction structure, FIGS. 21 to 23 arediagrams for explaining the manufacture of other types of spintronicselements of the quad junction structure, FIGS. 24A and 24B are diagramsfor explaining the manufacture of a spintronics element having thedouble reference structure, and FIGS. 25A and 25B are diagrams forexplaining the manufacture of a magnetic domain wall motion type memoryelement.

As shown in FIG. 19A, in the double junction structure W10 a, if therespective layers are simply stacked from the bottom, crystal propertiessuch as crystallinity and crystal orientation of an MgO uppermost layerwould degrade. In this example, on the other hand, as shown in FIG. 19B,a spintronics element substrate W10 (WA10+WB10′) is formed by placing afirst spintronics element substrate WA10 having a protection layer (notshown) formed on the MgO uppermost layer 20 and a second spintronicselement substrate WB10 having a cap layer, (CoFeB layer in this example)as an uppermost layer WB10 a in the same equipment as described above,removing all but of one-atomic layer of the protection layer of thefirst spintronics element substrate WA10 (not shown), binding the firstspintronics element substrate WA10 with the second spintronics elementsubstrate WB10, and removing the uppermost layer WB10 a, i.e., the caplayer of the second spintronics element substrate WB10 by etching. Thesecond spintronics element substrate in which the uppermost layer WB10 ais removed is shown as WB10′ in FIG. 19B. This manufacturing methodprovides spintronics elements W10 with excellent crystal propertiesincluding crystallinity and crystal orientation. Specifically, when theprotection layer of the first spintronics element substrate WA10 isremoved, a one-atomic CoFe layer is left on the MgO uppermost layer, asexplained initially with respect to exemplary embodiments 1 and 2. Amicrostructure between the MgO layer and the CoFe layer isMgO(001)[001]//CoFe(001)[011], whereby the crystal orientation of thespintronics element W10 is improved.

As shown in FIG. 20A, in the quad junction structure W20 a as well, themethod of simply stacking the respective layers from the bottom wouldcause the crystal properties such as crystallinity and crystalorientation explained above to get worse in upper layers. In thisexample, on the other hand, as shown in FIG. 20B, a spintronics elementW20 (WA20+WB20′) is formed by binding a first spintronics elementsubstrate WA20 having a protection layer (not shown) formed on theuppermost MgO layer 20 with a second spintronics element substrate WB20,and removing the uppermost layer, i.e., the cap layer WB20 a, (CoFeBlayer in this example) of the second spintronics element substrate WB20by etching. The second spintronics element substrate in which theuppermost layer WB20 a is removed is shown as WB20′ in FIG. 20B Thisway, it is possible to obtain the spintronics element W20 with evenupper layers having excellent properties such as crystallinity andcrystal orientation explained above.

The number of substrates to be bound is not limited to two, and as shownin FIG. 21 or 20, three or more spintronics element substrates, such asthe first to third spintronics element substrates WA20, WC20, and WD20,or the first to third spintronics element substrates WE20, WF20, andWG20, may be bound together to form one spintronics element.Furthermore, as shown in FIG. 23, the first to fourth spintronicselement substrates WH20, WI20, WJ20, and WK20 may be bound together. Aprotection layer needs to be formed on the substrate having the MgOuppermost layer, and in the process of removing the protection layer,one-atomic layer needs to be left.

As shown in FIG. 24A, in the double reference structure W30 a as well,the method of simply stacking the respective layers from the bottomwould cause the crystal properties such as crystallinity and crystalorientation explained above to get worse in upper layers. In thisexample, on the other hand, as shown in FIG. 24B, by binding a firstspintronics element substrate WA30 having a protection layer (not shown)formed on the uppermost MgO layer 20 with a second spintronics elementsubstrate WB30, it is possible to obtain a spintronics element W30 inwhich even upper layers have excellent properties such as crystallinityand crystal orientation explained above.

As shown in FIG. 25A, in a magnetic domain wall motion memory elementstructure W40 a having a magnetic domain wall motion layer, the MgOlayer and the CoFeB layer formed on the magnetic domain wall motionlayer are affected by the magnetic domain wall motion layer and theorientation thereof would degrade. To solve this problem, as shown inFIG. 25B, by placing a first spintronics element substrate WA40 having amagnetic domain wall motion layer and a second spintronics elementsubstrate WB40 having another layer structure and protection layer (notshown) in the same equipment, removing the protection layer of thesecond spintronics element substrate WB40 so as to leave one-atomiclayer, and binding the second spintronics element substrate WB40 withthe magnetic domain wall motion layer, a spintronics element W40 havingan excellent magnetic characteristic such as the TMR (tunnel magnetresistance effect) can be obtained. Alternatively, as shown in FIG. 25C,by binding a first spintronics element substrate WC40 having a magneticdomain wall motion layer, MgO layer and protection layer (not shown) inthis order with a second spintronics element substrate WD40 havinganother layer structure, a spintronics element W40 having excellentmagnetic characteristic such as TMR (tunnel magnet resistance effect)can be obtained.

When the magnetic direction is perpendicular, the magnetic domain wallmotion layer is made of a multi-layer structure of Co/Ni, for example,(S. Fukami, et al., IEEE Trans. Magn. 50, 3401006 (2014)), a multi-layerstructure of Ta layer/Ru layer/CoCrPt layer/Pt layer laminated in thisorder from the lower layer (H. Tanigawa, et al., Appl. Phys. Exp. 1,011301 (2008)), or a multi-layer structure of Ta layer/CoFeB layer/MgOlayer/Ta layer laminated in this order from the lower layer (S. Fukami,et al., Appl. Phys. Lett. 98, 082504 (2011)). When the magneticdirection is horizontal, the magnetic domain wall motion layer is madeof a NiFe layer, for example (H. Numata, et al., VLSI Technology, Symp.232 (2007)).

The MTJ manufactured by the binding process of this example ischaracterized by the fact that, in the case of the single MTJ, forexample, the ferromagnetic layer (CoFeB) under the Ta layer does nothave a layer having no magnetization (or dead layer). FIGS. 26A and 26Bare diagrams for explaining the dead layer. In a substrate W50 amanufactured by a method of simply stacking the respective layers as inthe conventional method, when a Ta layer is formed on a CoFeB layer, adead layer 200 is formed in the CoFeB layer, which causes a problem insome cases. As shown in FIG. 26A, when a Ta layer is formed on the upperCoFeB layer, for example, the dead layer 200 not having magnetization ofabout several angstroms (Å) is formed in a part of the CoFeB layeradjacent to the Ta layer. This dead layer 200 is not formed between thelower CoFeB layer and the Ta layer in the lower part (see S. Ikeda, etal., Mat. Mater. 9, 721 (2010)). Similar problems might arise when a Rulayer is to be formed as the cap layer (see S. Y. Jang, et al., J. Appl.Phys. 107, 09C707 (2010)). The formation of the dead layer can besuppressed by forming a NiFeHf layer as the cap layer or the like, butit is difficult to completely eliminate the dead layer (see U.S. Pat.No. 8,378,330 B2). On the other hand, as shown in FIG. 26B, when thesubstrate W50 is manufactured by binding the first substrate WA50 withthe second substrate WB50 using the binding method of the aboveembodiment 4, the dead layer 200 is not formed between the upper CoFeBlayer and the upper Ta layer, and therefore, it is possible to obtain asubstrate W50 of higher quality.

As described above, according to the above embodiments, in themanufacturing process of spintronics elements having an MgO layer or thelike that changes in quality by the reaction with H₂O and CO₂, and whenthe manufacturing process requires the wafer having the MgO layer at theuppermost layer (spintronics element substrate) to be exposed to theatmosphere, by forming a CoFeB cap layer on the uppermost layer, thedegradation of the MgO uppermost layer can be suppressed. This allowsvarious processes to be conducted that would significantly degrade thecharacteristics of the spintronics element with the conventionalconfiguration.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, the invention is not limitedto these embodiments. It will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the claims.

What is claimed is:
 1. A structure used in the formation of aspintronics element, the spintronics element to include a plurality oflaminated layers, comprising: a substrate; a plurality of laminatedlayers formed on the substrate, an uppermost layer of the plurality oflaminated layers being a non-magnetic layer containing oxygen; and aprotection layer directly formed on the uppermost layer, the protectionlayer preventing alteration of characteristics of the uppermost layerwhile exposed in an atmosphere including H₂O, a partial pressure of H₂Oin the atmosphere being equal to or larger than 10⁻⁴ Pa, no other layerbeing directly formed on the protection layer.
 2. The spintronicselement according to claim 1, wherein the protection layer has athickness equal to or greater than 2 nm, and includes at least amaterial selected from the group of material consisting of Co, Fe and B.3. The spintronics element according to claim 2, wherein thenon-magnetic layer includes Mg and O.
 4. The spintronics elementaccording to claim 3, wherein a second uppermost layer of the pluralityof laminated layers, and the protection layer, are both made of a samematerial.
 5. The spintronics element according to claim 1, wherein theplurality of laminated layers include an underlayer and a ferromagneticlayer disposed on the underlayer.
 6. The spintronics element accordingto claim 5, wherein a magnetization direction of the ferromagnetic layeris fixed in a direction perpendicular to a surface of the ferromagneticlayer.
 7. The spintronics element according to claim 5, wherein amagnetization direction of the ferromagnetic layer is not fixed toeither an upward or downward direction that is perpendicular to asurface of the ferromagnetic layer.
 8. The spintronics element accordingto claim 1, wherein the plurality of laminated layers include anunderlayer, a first ferromagnetic layer disposed on the underlayer, anon-magnetic binding layer disposed on the first ferromagnetic layer,and a second ferromagnetic layer disposed on the non-magnetic bindinglayer.
 9. The spintronics element according to claim 8, wherein a firstmagnetization direction of the first ferromagnetic layer and a secondmagnetization direction of the second ferromagnetic layer are fixed in asame direction perpendicular to a surface of the ferromagnetic layer.10. The spintronics element according to claim 8, wherein a firstmagnetization direction of the first ferromagnetic layer and a secondmagnetization direction of the second ferromagnetic layer are fixed indirections perpendicular to a surface of the ferromagnetic layer, thefirst magnetization direction being a direction opposite to the secondmagnetization direction.
 11. The spintronics element according to claim8, wherein each of a first magnetization direction of the firstferromagnetic layer and a second magnetization direction of the secondferromagnetic layer is not fixed to either an upward or downwarddirection that is perpendicular to a surface of the ferromagnetic layer.12. The spintronics element according to claim 1, wherein the pluralityof laminated layers include a magnetic domain wall motion layer.
 13. Aspintronics element, comprising an underlayer; and four laminated layersformed by binding at least two wafers, including a first ferromagneticlayer formed on the underlayer, a non-magnetic layer formed on the firstferromagnetic layer, a second ferromagnetic layer formed on thenon-magnetic layer, and a cap layer formed on the second ferromagneticlayer, wherein a surface portion of the second ferromagnetic layerdirectly contacts the cap layer and is free of any layer having nomagnetization.